Tuning the Assembly Process of Polyaniline Nanofibers by Adjusting the Acidic Nature and Solution Acidity toward Enhancing Electrochemical Charge Storage

Having easy control of the morphology and structure as well as large-scale production, seed polymerization has exhibited great potential to fabricate polyaniline (PANI) nanofibers as high-performance electrode materials for the supercapacitors. Herein the self-assembly of oligomer seeds was first constructed by chemical oxidation of aniline in a dilution solution by regulating the acidity and especially the nature of inorganic acids including hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), and phosphoric acid (H 3 PO 4 ), and then the successive growth of PANI nanofibers was carried out at high aniline concentration in a HCl solution. It was found that the charge-storage ability of PANI nanofibers can be greatly affected by the nanofibrous morphology and chain orientation that are more strongly related to the self-assembly behavior of nanofibrous oligomers as the seeds. It is found that the nature and acidity of inorganic acids have only a slight influence on the morphology, but a significant change occurred in the structure of the resulting PANI nanofibers. Especially, the nanofibers prepared by using the seeds in a HCl solution with a pH value of 3 possess a maximum specific capacitance of 504 F·g –1 at a current density of 1 A·g –1, holding a capacitance retention value of 90% within the range of the current density from 1 to 10 A·g –1 . Furthermore, the symmetric supercapacitor with a sandwich structure was assembled that could deliver a maximum energy density of 17.8 Wh·kg –1 at a power density of 416.1 W·kg –1, accompanied by a capacitance retention value of 70.2% after 2000 cycles. Small-diameter and highly oriented chains as well as high conductivity are in favor of fast penetration of an electrolyte and ion diffusion along with a shortening of the charge-transfer distance, which could contribute to the strong charge-storage ability of PANI nanofibers.